They do make higher capacity AA batteries, so you could improve on the performance.

What I found is that the normal Duracell Batteries got extremely hot while they charge my phone, while the eneloop batteries got warm but were ok to touch.

With the unit 1.2 oz & (2) AA batteries 1.8 oz. the entire unit only weighs in at 3 oz.!! With an extra set of batteries still brings you in under 5 oz. So far this is the lightest weight option that I have found available. In addition, using rechargeable batteries that can be recharged up to 1500 times, saves money on batteries. You could put a charger in your bounce box if you really wanted to, but I’m thinking the rechargeables might be a better option for section hiking.

Featured Adafruit Product

MintyBoost Kit – v3.0: Make your own iPod/iPhone/GPS/etc… battery-pack and recharger! This project includes all the electronic parts necessary to build your own MintyBoost: a small & simple (but very powerful) USB charger for your iPod (or other mp3 player), camera, cell phone, and any other gadget you can plug into a USB port to charge. If you have a Nintendo DS/GBA or a PSP you can buy charger cables from us, too. The charger circuitry and 2 AA batteries fit into an small space such as an Altoids gum or mint tin, and will run your iPod for hours, 2.5x more than you’d get from a 9V USB charger! You can use rechargeable batteries too. (read more)